Filament Remaining Calculator | PrintCalcLab

Calculate remaining filament length from spool weight.

Running a spool dry halfway through a thirty-hour print is one of the most avoidable failures in 3D printing. Weight is the most reliable indicator of what is left, because length cannot be checked without unwinding the spool. This calculator turns net filament weight into remaining length using the material's density and the filament diameter, so you can compare the slicer's required length against what is actually on the spool before pressing print.

How It Works

The remaining length is the net weight divided by the mass per unit length, where mass per length is the density times the filament's circular cross-section. Weigh the spool, subtract the empty-spool weight, pick your material, and enter the diameter (1.75 mm or 2.85 mm). A full 1 kg of 1.75 mm PLA at 1.24 g/cm³ works out to roughly 335 meters. The calculator covers eight materials — PLA, ABS, PETG, TPU, Nylon, PC, ASA, and HIPS — and rejects zero or negative weights and diameters rather than returning misleading numbers.

FAQ

How do I find my empty spool's weight?

Check the manufacturer's specification — many print it on the spool label or list it online — or weigh a finished empty spool of the same brand. Spool weights differ noticeably between brands and between plastic and cardboard spools, so avoid reusing one number everywhere.

Why does the same weight give different lengths for different materials?

Density varies: a kilogram of ABS at 1.04 g/cm³ stretches to about 400 m of 1.75 mm filament, while denser PETG at 1.27 g/cm³ yields only about 327 m. Always select the actual material, not just the brand.

How much shorter is a 2.85 mm spool?

The 2.85 mm cross-section carries about 2.65 times more plastic per meter than 1.75 mm, so a 1 kg PLA spool holds roughly 126 m instead of about 335 m. Diameter enters the formula squared, which is why this input matters so much.

Is the result exact enough to risk a long print?

Treat it as a close estimate. Real diameter tolerance, moisture absorbed by the filament, and density variation between brands all shift the true length by a few percent, so leave a safety margin instead of planning to finish with meters to spare.